Rickettsiae are gram-negative, obligate intracellular bacteria that are transmitted to humans through arthropod vectors such as ticks, mites, lice, and chiggers. In India, rickettsial diseases are commonly found in the sub-Himalayan belt and states such as Jammu and Kashmir, Nagaland, Himachal Pradesh, Uttaranchal, Rajasthan, Assam, West Bengal, Maharashtra, Kerala, Tamil Nadu, and Delhi. Rickettsiae are classified into spotted fever group, typhus group, scrub typhus, ehrlichioses and anaplasmosis, and Q fever. Common symptoms include fever, rash, and headache

2. Geographical distribution in India
 Sub – himalyan belt -Jammu and Kashmir –
nagaland, Himachal Pradesh,
Uttaranchal, Rajasthan, Assam, West
Bengal, Maharashtra,
Kerala, Tamil Nadu and Delhi

3. Rickettsia
Gram-negative
bacilli
obligate
intracellular.

4. Groups
 Spotted fever group
Typhus group
 Scrub typhus
 Ehrlichioses and anaplasmosis
 Q fever

5. Arthropod vector
Tick
Except:
Epidemic typhus -
louse
Rickettsial pox – mite
Scrub typhus –chigger
Q fever – aeresol
inhalation ( no vector)

6. Host
 Dogs
Rodents
Except:
Epidemic typhus
- humans
Q fever - cattle,
goats, cats

7. Pathogenesis
Bite
Blood stream
Endothelium/vascular smooth muscles
Target cells
 Host defenses – T cell, TNF α, γ interferon

8. History
Removal of an attached tick ( 60%)
 Endemic area/ wooded area
 Season – July to October
 Similar illness in close contacts
Contact with dog

9. Clinical features
Incubation period – 2 – 14 day
Common symptoms:
Clinical triad
 Fever
 Rash - centripetal
Headache

10. Rash
Early stage:
Discrete, pale, rose red,
blanching maculopapular
on extremities
Late stage:
Petechial /haemorragic /
purpuric/Ecchymosies/
necrotic/ulcer

11. Eschar
red induration
Enlarge
Vesiculates
Ruptures
Eschar
3 – 4 wks
Resolves

12. Others symptoms:
 Lympadenopathy
 Hepatospleenomegaly
 Edema
 Conjunctival congestion
 Gastrointestinal symptoms – emesis, pain
 CNS involvement
 Pulmonary infiltrates – Q fever
 Infectious mononucleosis like syndrome - ehrelichia

13. Complication
 CNS - Cerebral edema, Meningoencephalitis
Neurologic sequelae,
 RS -Noncardiogenic pulmonary edema,
consolidation
CVS - vascular collapse, Myocarditis
RENAL - acute renal failure
 LIVER - Hepatic dysfunction
Multiorgan damage

14. Fulminant RMSF
Death< 5 days
G6PD deficiency individuals
DIC
Liver/ renal/ respiratory failure

15. Common lab abnormalities
 Increased AST and ALT
 Decreased platelets
 Decreased Na (+/-)
 Decreased WBC (+/-), left shift
 Interstital infiltrate ( Qfever)
 Atypical lymphocytosis (sennetsu
ehirlichiosis)

16. Diagnostic tests
Early
Immunohistochemistry of skin biopsy
 Direct fluorescent antibody test
PCR
After 1 wk
 Indirect fluorescent antibody test – Gold
standard
4 fold increase/ titre of >64

17. Other investigations
Immunoperoxidase assay
 Lattex agglutination test
 Indirect haemagglutination test
 ELISA
 Dot – blot immunoassay
Weil – Felix – high specific/low sensitive

18. Treatment
Doxycycline (2.2 mg/kg/dose bid PO or IV,
maximum 200 mg/day) - DOC
Tetracycline (25–50 mg/kg/day divided
every 6 hr PO, maximum 2 g/day)
 Chloramphenicol (50–100 mg/kg/day
divided every 6 hr IV, maximum 3 g/day)

19.  Azithromycin – doxycycline resistant
 Clarithromycin
 Fluroquinolones
Trimethoprim – sulfamethoxazole
 Rifampicin – scrub typhus